Why can't I sign into my Apple ID?

And you are sign in here . . . .

See the following Apple articles:

If you can't connect or sign in to iCloud

If you can't connect or sign in to iCloud - Apple Support

Get help with security issues

Get help with security issues - Apple Support

Have you forgotten your password? -> See this Apple article: If you forgot your Apple ID password

If you forgot your Apple ID password - Apple Support

Then see this Apple article: What to do after you change your Apple ID or password

What to do after you change your Apple ID or password - Apple Support

Where are you trying to sign in? Does the app/web site accept Sign in with Apple ID?

What is Sign in with Apple?   *

Sign in with Apple ID - How to use.    *

Sign in with Apple - Manage the apps you use with.   *